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Full text of "Treatise On Applied Analytical Chemistry(Vol-1)"

PHOSPHATES

129

50 c.c. of the filtrate (= i gram of substance) are shaken in another 250 c.c.
flask with 50 c.c. of water and 25 c.c. of cone, sulphuric acid, allowed to
stand for about 15 minutes and then well shaken with 100 c.c. of 95-96%
alcohol. When quite cold, the liquid is made up to volume with alcohol,
mixed and again made up to volume (contraction'occurring) ; after mix-
ing, the solution is left for at least 30 minutes and filtered. 100 c.c. of the
filtrate (= 0-4 gram of substance) are evaporated almost to dryness in a
porcelain dish and the residue taken up in water,1 heated on a water-bath
and treated with a slight excess of ammonia, which precipitates the iron
and aluminium as phosphates. The heating is continued until the excess
of ammonia is expelled, the liquid being filtered when cold and the precipi-
tate washed with hot water, dried, ignited and weighed. The weight,
divided by 2, gives Fe203 + A1203 in 0-4 gram of substance.

5. Other Determinations.—For complete analysis, which is required
more especially with mineral phosphates, the determinatijns indicated
briefly below 2 are necessary in addition to those given above :

Fluorine, by transformation into silicon fluoride by treatment with
silicious sand and sulphuric acid, the fluoride being subsequently decom-
posed by water and the hydrofluosilicic acid formed titrated (Penfield's
or Offermann's method).

Chlorine, by dissolving the phosphate in nitric acid and estimating the
chlorine volumetrically by the usual methods.

Sulphuric acid, by precipitation as barium sulphate from the hydro-
chloric acid solution of the phosphate.

Carbon dioxide, by treatment of the phosphate with an acid and absorp-
tion of the carbon dioxide by potassium hydroxide in the usual manner.

Silica, by treatment of the substance with aqua regia so as to render the
silica insoluble.

Manganese, by dissolving the substance in aqua regia, eliminating the
iron, phosphates, etc., by means of zinc oxide and titration of the mangan-
ous salt, remaining in solution, with permanganate.

Lime, by weighing the calcium sulphate remaining undissolved in alcohol
in the determination of the oxides of iron and alumina by Glaser's method
(see 4), or by dissolving the substance in hydrochloric acid, precipitating
with ammonia, redissolving in acetic acid and separating the lime as oxalate.

Magnesia, by precipitation as magnesium ammonium phosphate after

elimination of the lime.

*
* *

Mineral phosphates may contain (%) : moisture, 0-3-8 ; P2O5, 10-55 ; CaO,
22-57 .' A12O3 + Fe2O3, 0-2-10 ; CO2, 2-24 ; SiO2, 2-8. Small amounts of
fluorine (more than 0-1% CaF2) and manganese are almost always present.

Bones and bone ash may contain 37-40% P2O5, and up to about 4% N.

Bone black  (refinery waste,  etc.) usually contains   20-40% of water and

25-30% P2o5-

1  If the phosphate contains organic substances, it is well at this point to take up
with hydrochloric acid and a few drops of bromine, to boil until bromine vapours dis-
appear, to dilute with water, and to precipitate with ammonia as above.

2  The detailed methods may be found in special works dealing with the analysis of
fertilisers or, more particularly, of phosphates.

A.C.                                                                                                               9g then made up and the